Mechanical and chemical-mechanical planarizing processes ("CMP") are used in the manufacturing of electronic devices for forming a flat surface on semiconductor wafers, field emission displays and many other microelectronic-device substrate assemblies. CMP processes generally remove material from a substrate assembly to create a highly planar surface at a precise elevation in the layers of material on the substrate assembly.
FIG. 1 schematically illustrates an existing web-format planarizing machine 10 for planarizing a substrate 12. The planarizing machine 10 has a support table 14 with a top-panel 16 at a workstation where an operative portion (A) of a planarizing pad 40 is positioned. The top-panel 16 is generally a rigid plate to provide a flat, solid surface to which a particular section of the planarizing pad 40 may be secured during planarization.
The planarizing machine 10 also has a plurality of rollers to guide, position and hold the planarizing pad 40 over the top-panel 16. The rollers include a supply roller 20, first and second idler rollers 21a and 22b, first and second guide rollers 22a and 22b, and a take-up roller 23. The supply roller 20 carries an unused or pre-operative portion of the planarizing pad 40, and the take-up roller 23 carries a used or post-operative portion of the planarizing pad 40. Additionally, the first idler roller 21a and the first guide roller 22a stretch the planarizing pad 40 over the top-panel 16 to hold the planarizing pad 40 stationary during operation. A motor (not shown) drives at least one of the supply roller 20 and the take-up roller 23 to sequentially advance the planarizing pad 40 across the top-panel 16. As such, clean pre-operative sections of the planarizing pad 40 may be quickly substituted for used sections to provide a consistent surface for planarizing and/or cleaning the substrate 12.
The web-format planarizing machine 10 also has a carrier assembly 30 that controls and protects the substrate 12 during planarization. The carrier assembly 30 generally has a substrate holder 32 to pick up, hold and release the substrate 12 at appropriate stages of the planarizing cycle. A plurality of nozzles 33 attached to the substrate holder 32 dispense a planarizing solution 44 onto a planarizing surface 42 of the planarizing pad 40. The carrier assembly 30 also generally has a support gantry 34 carrying a drive assembly 35 that translates along the gantry 34. The drive assembly 35 generally has an actuator 36, a drive shaft 37 coupled to the actuator 36, and an arm 38 projecting from the drive shaft 37. The arm 38 carries the substrate holder 32 via another shaft 39 such that the drive assembly 35 orbits the substrate holder 32 about an axis B--B offset from a center point C--C the substrate 12.
The planarizing pad 40 and the planarizing solution 44 define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the substrate 12. The planarizing pad 40 used in the web-format planarizing machine 10 is typically a fixed-abrasive planarizing pad in which abrasive particles are fixedly bonded to a suspension material. In fixedabrasive applications, the planarizing solution is a "clean solution" without abrasive particles because the abrasive particles are fixedly distributed across the planarizing surface 42 of the planarizing pad 40. In other applications, the planarizing pad 40 may be a non-abrasive pad without abrasive particles composed of a polymeric material (e.g., polyurethane) or other suitable materials. The planarizing solutions 44 used with the non-abrasive planarizing pads are typically CMP slurries with abrasive particles and chemicals to remove material from a substrate.
To planarize the substrate 12 with the planarizing machine 10, the carrier assembly 30 presses the substrate 12 against the planarizing surface 42 of the planarizing pad 40 in the presence of the planarizing solution 44. The drive assembly 35 then orbits the substrate holder 32 about the offset axis B-B to translate the substrate 12 across the planarizing surface 42. As a result, the abrasive particles and/or the chemicals in the planarizing medium remove material from the surface of the substrate 12.
CMP processes should consistently and accurately produce a uniformly planar surface on the substrate assembly to enable precise fabrication of circuits and photo-patterns. During the fabrication of transistors, contacts, interconnects and other features, many substrate assemblies develop large "step heights" that create a highly topographic surface across the substrate assembly. Yet, as the density of integrated circuits increases, it is necessary to have a planar substrate surface at several stages of processing the substrate assembly because non-uniform substrate surfaces significantly increase the difficulty of forming sub-micron features. For example, it is difficult to accurately focus photopatterns to within tolerances approaching 0.1 .mu.m on non-uniform substrate surfaces because sub-micron photolithographic equipment generally has a very limited depth of field. Thus, CMP processes are often used to transform a topographical substrate surface into a highly uniform, planar substrate surface.
In the competitive semiconductor industry, it is also highly desirable to have a high yield in CMP processes by quickly producing a uniformly planar surface at a desired endpoint on a substrate assembly. For example, when a conductive layer on a substrate assembly is under-planarized in the formation of contacts or interconnects, many of these components may not be electrically isolated from one another because undesirable portions of the conductive layer may remain on the substrate assembly over a dielectric layer. Additionally, when a substrate assembly is over planarized, components below the desired endpoint may be damaged or completely destroyed. Thus, to provide a high yield of operable microelectronic devices, CMP processing should quickly remove material until the desired endpoint is reached.
The web-format machine 10 produces good results in applications that use a stationary planarizing pad 40 and orbit the substrate assembly 12 about the offset axis B--B. One problem of CMP processing that the planarizing machine 10 addresses is the center-to-edge planarizing profile produced by conventional planarizing machines that have a rotating platen and a substrate holder that rotates about the center point of the substrate. In conventional rotating platen machines, the rotation of both the planarizing pad and the substrate holder causes the relative velocity between the substrate assembly and the pad to be consistently higher at the perimeter of the substrate assembly than the center. The polishing rate accordingly varies from the center of the substrate assembly to the perimeter causing a center-to-edge planarizing profile. The webformat machine 10 reduces the center-to-edge planarizing profile by orbiting the substrate holder 32 about the offset axis B-B and holding the planarizing pad 40 stationary to reduce the difference in relative velocity between the substrate assembly 12 and the pad 40 across the surface of the substrate assembly 12.
The web-format planarizing machine 10 also produces highly planar surfaces when substrate assemblies are planarized on a fixed-abrasive planarizing pad 40 and a "clean" planarizing solution 44, i.e., a planarizing solution without abrasive particles. Because the abrasive particles are fixedly bonded to the pad 40, the particles cannot agglomerate in the planarizing solution or accumulate on the planarizing surface in waste matter accumulations. The fixed distribution of abrasive particles on the pad also provides a desired distribution of abrasive particles under the substrate assembly that is not a function of the distribution of the planarizing solution under the substrate assembly. Thus, the planarizing machine 10 is particularly usefull in applications that orbit a substrate across a stationary fixed-abrasive pad in the presence of a clean planarizing solution.
Although the web-format planarizing machine 10 is particularly useful for fixed-abrasive applications with clean planarizing solutions, it may also be desirable to use the web-format machine 10 with non-abrasive planarizing pads and slurries having abrasive particles. One reason for using the planarizing machine 10 with non-abrasive pads and abrasive slurries is that fixed-abrasive planarizing pads and clean planarizing solutions may not be available for the structures and chemistries required for many CMP applications. For example, fixed-abrasive pads and clean solutions used to planarize a metal layer of aluminum, copper, tungsten, or titanium in the formation of highly conductive interconnects are not widely available for the web-format machine 10. Thus, many CMP applications may require the use of web-format machines 10 with non-abrasive pads and abrasive slurries.
One drawback of CMP, and particularly the planarizing machine 10, is that it is difficult to planarize metal layers using non-abrasive pads and abrasive slurries. CMP of metal layers generally involves oxidizing the surface of the metal layer with oxidants in the slurry, and removing the oxidized metal ions from the metal layer with the abrasive particles in the slurry. The metal ions removed from the substrate 12, however, may become reattached to the substrate 12 where they can create current leakage paths or other defects. In applications with high ionization rates or in which the slurry accumulates on the polishing pad, the likelihood that metal ions will reattach to the substrate surface increases because the concentration of metal ions in the slurry increases. Thus, planarizing metal layers using the web-format planarizing machine 10 or machines having slow moving polishing pads may cause significant defects that reduce the yield of operable microelectronic devices.
Another drawback of planarizimg substrate assemblies using non-abrasive pads and abrasive slurries is that the abrasive particles may accumulate on the pad or agglomerate in the slurry. These problems are particularly present when planarizing metal layers on the stationary pad of the web-format planarizing machine 10. The accumulations of abrasive particles on the planarizing pad 40 typically alter the abrasiveness of the planarizing pad, and thus they also alter the consistency of the polishing rate across the planarizing pad. Additionally, the agglomerations of the abrasive particles in the slurry may alter the abrasiveness of the slurry. In extreme cases, the agglomerations of the abrasive particles in the slurry may scratch the surface of the substrate 12. Therefore, the web-format planarizing machine 10 may not produce sufficiently planar substrate assemblies and/or may produce defects in the substrate assemblies when planarizing metal layers with non-abrasive planarizing pads and abrasive slurries.